1. Field of the Invention
The invention relates to varying the relative setting angle .beta. of vibration generators having at least two pairs of part unbalance elements that can be adjusted in relation to each other.
2. Description of the Prior Art
Adjustable vibration generators are described in published International Application WO91/08842 and in PCT/EP90/02239. In the description of the present invention, for the purpose of simplification, the same terminology is employed as is used in the last-mentioned publication, relating to the part unbalance elements and the partial centrifugal forces (or partial centrifugal force vectors) associated with such elements, as well as relating to a "pair" of part unbalance elements. By comparison with the publications cited above, the relative setting angle .beta. is defined below in such a way that the value .beta.=0.degree. corresponds to an oscillatory amplitude of zero, and the value .beta.=180.degree. corresponds to a maximum oscillatory amplitude.
The relative setting angle .beta. of an adjustable vibration generator is theoretically defined between the partial centrifugal force vectors of the individual part unbalance elements of a "pair" of part unbalance elements. In practice, it is also possible to define the relative setting angle .beta. between features (for example geometric features) of the part unbalance elements of a pair, provided that the position of the mass center of gravity of the eccentric mass of each element is known. The identifier "MR" is commonly used for the reaction moments "MR" which, during each unbalance rotation through the rotation angle .mu.=2.pi., occur twice as alternating moments at the shafts of the part unbalance elements [these alternating moments have a sinusoidal waveform with two minimum and two maximum values per revolution of the part unbalance element].
The average reaction moments, which act in only one direction and can be calculated by integrating MR over the angle of rotation .mu.=2.pi. and by subsequent division of the integration value by 2.pi., are referred to as "MRQ". As will be apparant to those skilled in the art, for example from above-referenced WO91/08842, in the event of a relative setting angle being set to 0.degree.&lt;.beta.&lt;180.degree., these average reaction moments MRQ act on the part unbalance elements of a pair in such a way that the reaction moments MRQ of one kind try to accelerate the rotation of the part unbalance elements of one kind, and the reaction moments MRQ of the other kind try to retard the rotation of the part unbalance elements of the other kind. In the case of a 4-shaft unbalance vibrator having a motor coupled to each shaft, this mode of operation leads to the situation where, in the case of a vibrator that is operating at idle with a relative setting angle set to be 0.degree.&lt;.beta.&lt;180.degree., two of the motors have to operate as motors and two of the motors have to operate as generators. Reference is made at this point to the fact that, for the description "unbalance moment", further descriptions, such as "static moment" are also known to those skilled in the art.
FIG. 1 of published German Patent Application 43 01 368 shows a hydraulically operated "gearless vibrator" with an adjustable unbalance moment, with the first motors 103 and 104 that belong to the first part unbalance elements and the second motors 107 and 108 that belong to the second part unbalance elements. The first two motors are supplied in parallel and at the same input pressure by a volume flow that is generated by the adjustable pump 114. The second two motors are each connected to a first motor by means of a series circuit. This is a so-called open circuit for the fluid medium.
The range of adjustment for the unbalance moment in the arrangement of DE A 43 01 368 is limited to an angle 0.degree..ltoreq..beta..ltoreq.90.degree.. The vibrator shown is provided with the capability of maintaining the mirror-image synchronous running of the angle of rotation of part unbalance elements of the same kind, even under the influence of the disruptive forces that are generally to be expected, but at least over that range of adjustment in which the maximum unbalance moment can be set. This capability is viewed as derived from the effects of those alternating moments which are produced by the reaction moments MR and which are also originally responsible for the production of the average reaction moments MRQ. In the DE A 43 01 368, nothing is stated about the behavior of the stability of the mirror-image synchronous running of the part unbalance elements of the same kind in each case during the conceivable use of another kind of control for the angle .beta. for a range of adjustment 90.degree..ltoreq..beta..ltoreq.180.degree.. In the event of a closer inspection of the configuration shown, it is possible to demonstrate that, when operating at the maximum unbalance moment (which is more likely the normal case, given the envisaged range of use of the invention), taking into account the "pressure sum", the first motors are loaded more than two and a half times as much as the second motors. In this case, the "pressure sum" is the sum of input pressure and output pressure at the motor, which is decisive for the service life of the motors.
In the case of the vibrator shown, in addition to the extremely asymmetrical loading of the motors, it has to be viewed as an additional disadvantage that, for the purpose of achieving comparably large resultant unbalance moments, the partial unbalance moments of the part unbalance elements have to be dimensioned to be larger than normal. This leads to unnecessarily increased bearing forces and reaction torques MRQ.
In the case of the vibrators described using FIGS. 1 and 4, DE A 43 01368 methods of influencing the motors for the purpose of setting a predefined relative setting angle .beta. are used with which, in fact, it is not possible to open up a range of adjustment from .beta.=90.degree. to .beta.=180.degree.. As will be shown later, the methods described primarily suffer from the fact that they have not taken into account the influence of the bearing frictional power and of the useful power, which is important in practice.
As noted above, WO91/08842 is of general interest in establishing the state of the prior art. It is particularly noteworthy that the throttling, shown in FIG. 1, of the volume flow passing through the motor 116, said throttling being carried out using the pressure limiting valve 124, cannot lead (starting from a position in which the resultant unbalance moment has the value zero) to changing the relative setting angle .beta. in such a way that the resultant unbalance moment is increased. In order to be able to achieve this effect truly, it would be necessary, with the aid of the function of the element 124, to effect a pressure rise between input and output of the motor 116, while at the same time a reduction in the pressure takes place between the input and output of the motor 114. For the purpose of satisfying the desired function, it would also be necessary in this case to satisfy the condition that the measurable pressure at the input of motor 114 is greater than the measurable pressure at the input of motor 116. This requirement cannot be satisfied on its own (given necessarily equally large volume flows through the two motors), since both the volume flows are taken from a common source (122). FIG. 1 therefore more likely serves in fact to describe the expressions used.
German patent 41 16 647: discloses an adjustable, gearless prior art vibrator with electric motors, each motor being assigned its own electronic regulating device. For each motor, there is a measuring device using which the relative angular position of all the part unbalance elements in relation to one another can be measured continuously. In this case, the angle of rotation of a first part unbalance element is defined as a reference position, and the angles of rotation of the remaining three part unbalance elements are measured as relative angles in relation to the first part unbalance element. In the case of this solution, the individual regulation of the angle of rotation of each part unbalance element means that, in addition to setting the given relative setting angle .beta., the mirror-image symmetrical rotation angle position between the part unbalance elements of the same kind is also maintained at the same time. This solution is not suitable for use in ram vibrators, and not just because of the enormously high complexity. However, the solution shown gives a good example of the many ways in which loading of the 4 motors of a controllable, gearless vibrator can be carried out.
Published German Application 44 07 013 also makes reference to gearless vibrators. However, the appropriate note on page 6, lines 3 to 8, only reiterates technical details which are already known from DE-A 43 01 368. Reference may also be made to the fact that patent claim 3 does not relate to gearless vibrators. The preamble to this patent claim already rules out any use in gearless vibrators, since the rotors of the adjusting motors are intended to be connected to more than one part unbalance element in each case. In addition, it is possible to derive from the defining part of patent claim 3 (first feature) the fact that the adjusting motors cannot at the same time be drive motors.
A description is given in published German Application 44 25 905 of a technique which can be used, in particular in the case of gearless vibrators in which the resultant unbalance moment can be adjusted, with additional measures to force the synchronous running from a relative angle of rotation which may be defined between the part unbalance elements of the same kind. DE A 44 25 905 also makes reference to the problems of maintaining synchronous running of the relative angle of rotation between the part unbalance elements of the same kind.